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Questions and Answers
In an ionic solid, what is the primary force holding the ions together?
In an ionic solid, what is the primary force holding the ions together?
- Magnetic forces
- Nuclear forces
- Gravitational forces
- Electrostatic attractions (correct)
What is a 'unit cell' in the context of ionic compounds?
What is a 'unit cell' in the context of ionic compounds?
- The total number of ions in a crystal
- The largest repeating unit in a crystal lattice
- The smallest repeating unit in a crystal lattice (correct)
- A single molecule of the ionic compound
What is the coordination number of $Cs^+$ in the Cesium Chloride ($CsCl$) structure?
What is the coordination number of $Cs^+$ in the Cesium Chloride ($CsCl$) structure?
- 12
- 8 (correct)
- 4
- 6
Which of the following statements correctly describes the Cesium Chloride ($CsCl$) structure?
Which of the following statements correctly describes the Cesium Chloride ($CsCl$) structure?
In the Rock Salt (NaCl) structure, what type of holes do the sodium ions ($Na^+$) fit into?
In the Rock Salt (NaCl) structure, what type of holes do the sodium ions ($Na^+$) fit into?
What is the coordination number of $Cl^-$ in the Sodium Chloride ($NaCl$) structure?
What is the coordination number of $Cl^-$ in the Sodium Chloride ($NaCl$) structure?
In the Zinc Blende (ZnS) structure, what fraction of tetrahedral holes are occupied?
In the Zinc Blende (ZnS) structure, what fraction of tetrahedral holes are occupied?
What is a key characteristic of the Fluorite ($CaF_2$) structure regarding the location of the cation ($Ca^{2+}$)?
What is a key characteristic of the Fluorite ($CaF_2$) structure regarding the location of the cation ($Ca^{2+}$)?
In the Fluorite ($CaF_2$) structure, what is the coordination number of the fluoride ion ($F^-$)?
In the Fluorite ($CaF_2$) structure, what is the coordination number of the fluoride ion ($F^-$)?
How does the arrangement of ions in the antifluorite structure ($Li_2O$) compare to that of the fluorite structure ($CaF_2$)?
How does the arrangement of ions in the antifluorite structure ($Li_2O$) compare to that of the fluorite structure ($CaF_2$)?
Flashcards
Crystal Structure
Crystal Structure
A repeating arrangement of atoms, molecules, or ions in a solid.
Coordination Number
Coordination Number
The number of ions surrounding a central ion in a crystal lattice.
Unit Cell
Unit Cell
The smallest repeating unit within a crystal lattice that retains the structure's symmetry.
Cesium Chloride Structure
Cesium Chloride Structure
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Rock Salt Structure
Rock Salt Structure
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Zinc Blende Structure
Zinc Blende Structure
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Fluorite Structure
Fluorite Structure
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Antifluorite Structure
Antifluorite Structure
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Anion
Anion
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Study Notes
Structures of Ionic Solids
- Involve two or more ions
- Oppositely charged ions are held together with electrostatic attractions
- Attractive forces are maximized when each ion is surrounded by ions of opposite charge
- Form 3D crystal structures with alternating ions
- The sum of all the positive charges equals the sum of all the negative charges
Coordination Numbers
- Describes the number of ions surrounding a central ion
- Cation Coordination Number (CN) = the number of anions surrounding the cation
- Anion Coordination Number = the number of cations surrounding the anion
- Coordination numbers of both ions are the same unless the number of ions differ like in NaCl vs CaCl₂
- A unit cell for an ionic compound is the smallest repeating unit, usually a "face" of the unit cell
Cesium Chloride Structure (CsCl)
- Body-centered structure with Cesium (Cs⁺) cations filling cubic holes in the center of the cube
- Ratio of 1:1
- Coordination Number (CN) of Cs⁺ = 8 Cl⁻ anions since Cs⁺ is surrounded by 8 Cl⁻ anions in a cubic arrangement
- There are 2 atoms
- 1 Cesium
- 1 Chlorine
- 1 Cs⁺ Cation in the center of the cube
- 1 Cl⁻ anion at each of the 8 corners * ⅛ = 1 Cl⁻ anion
- Cl⁻ coordination number is 8, and the structure is surrounded by 8 Cs⁺ cations
- The structure is BCC
- Cs⁺ coordination number is 8
Rock Salt/Sodium Chloride Structure (NaCl)
- The structure is face-centered and has 2 hole types
- There are 8 atoms
- 4 Chlorine
- 4 Sodium
Octahedral Holes
- Each hole is surrounded by 6 spheres
- The CN is 6
- The holes are larger than tetrahedral holes
Tetrahedral Holes
- Each hole is surrounded by 4 spheres
- A cation in a tetrahedral hole is surrounded by 4 anions
- CN = 4
- There are 2x as many tetrahedral holes as octahedral holes
Cubic-Close Packed (FCC) Arrangement
- Cl⁻ ions are in a face-centered cubic arrangement
- Na⁺ ions fit into octahedral holes
- CN of Cl⁻ = 6, with 4 Cl⁻ anions
- CN of Na⁺ = 6, with 4 Na⁺ cations
Zinc Blende/Zinc Sulfide Structure (ZnS)
- A face-centered structure with 8 tetrahedral holes
- Zinc (Zn²⁺) actually only occupies half of the tetrahedral holes, so only 4
Ions
- Has Zinc Ions (Zn²⁺) and Sulfide Ions (S²⁻)
- Zn²⁺ ions positioned internally are completely inside the unit cell
- CN: 4
- 4 Sulfide ions occupies half of the 8 tetrahedral holes
- CN: 4
- Has 8 atoms
- 4 Zn²⁺
- 4 S²⁻
Fluorite/Calcium Fluoride Structure (CaF₂)
- A face-centered structure with 8 tetrahedral holes
- For cation "face"
- Ratio of 2 Fluoride to every calcium
- Calcium ions (Ca²⁺) are surrounded by 8 Fluoride anions
- CN = 8
- Fluoride fills all 8 tetrahedral holes
- 12 atoms
- 4 Calcium
- 8 Fluoride
Antifluorite Structure (Li₂O)
- A face-centered structure with 8 tetrahedral holes
- Lithium (Li⁺) cation surrounded by 4 Oxide (O²⁻) anions
- CN = 4
- 4 cubic
- Oxide (O²⁻) ions are surrounded by 8 Lithium (Li⁺) cations
- CN = 8
- Has 12 atoms
- 8 Lithium
- 4 Oxide
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